The present invention relates to an image forming apparatus such as an electrophotographic apparatus, an electrostatic recording apparatus, and the like, in particular, an image forming apparatus comprising a fixing device for fixing developer such as toner to recording paper.
In the field of an image forming apparatus, such as a copying apparatus, a printer, or the like, employing an electrophotographic or electrostatic recording method, it is common practice to thermally fix an unfixed image formed on a recording medium, for example, paper, to the recording medium with the use of a fixing device.
A fixing device used for the above described purpose usually comprises a heat roller as a thermal fixing member, and a pressure roller. The heat roller internally holds a heater. The pressure roller rotates while being kept in contact with the heat roller with a predetermined amount of pressure. In order for an image forming apparatus to be superior in terms of fixing performance, the temperature of the fixing roller must be kept at a proper level.
Thus, in order to prevent the fixing device from abnormally heating, the control section monitors the temperature of the fixing roller with the use of a temperature sensor such as a thermistor. Even when a fixing device anomaly, for example, overheating, is detected, the anomaly, or the abnormal temperature of the fixing roller, sometimes continues because a user turns off, and then, turns on, the power source to the image forming apparatus, in an attempt to restart the apparatus in order to restore the fixing device. In the past, in order to prevent the above described phenomenon, the data regarding the fixing device anomaly were written in a nonvolatile memory (EEPROM), or the like, and as the apparatus is restarted, the contents of this nonvolatile memory were checked. If the presence of the fixing device anomaly data was detected in the nonvolatile memory, control was executed so that electrical power was not supplied to the fixing heater.
In the case of an image forming apparatus such as the one described above, once fixing device anomaly data were written into the nonvolatile memory, the apparatus could not be normally started up, unless the fixing device anomaly data were eliminated. In order to eliminate the anomaly data, it was necessary to bring in a service person, or carry out a specific anomaly data elimination operation.
There are various fixing device anomalies, although their occurrences are quite rare. For example, there is the startup error which occurs when voltage remains abnormally low for an extended period of time. There is the heater xe2x80x9crunawayxe2x80x9d or excessive temperature increase, resulting from the malfunction of the control section caused by excessive noise or the like. Further, sometimes, the control section detects an abnormally high temperature due to the timing with which the power source to the apparatus is turned off, and then, turned on, after the detection of the truly abnormally high temperature, and therefore, falsely determines that the fixing device is in the abnormal state. As a fixing device anomaly such as those described above occurs, a service person or the like will be requested even if nothing is wrong with the apparatus itself.
The primary object of the present invention is to provide an image forming apparatus which is a highly reliable image forming apparatus.
Another object of the present invention is to provide an image forming apparatus, the operation of which is not suspended due to erratic anomaly detection.
Another object of the present invention is to provide an image forming apparatus, the operation of which can be reliably recovered by the turning off and on of the power source switch, even when there are fixing device anomaly data in the memory.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.